Body-fitted and embedded mesh techniques are combined to obtain accurate external aerodynamic solutions for realistic car geometries with minimal user intervention. The key idea is to mesh with typical body-fitted RANS grids the external shape of the vehicle, which is smooth and requires detailed physical modeling. The underhood and undercarriage are treated as embedded surfaces. The flow in this region is massively separated, requiring LES runs and isotropic grids. This makes it a suitable candidate for embedded grids. Comparisons with body-fitted and experimental data for a typical car show that this approach can yield drag predictions with an error less than 5%. Thus, the present approach reduces turnaround times for complete car geometries to 1-2 days, without compromising accuracy. I. INTRODUCTION With the advent of robust, accurate flow solvers and abundant, pervasive computer resources, the task of defining quickly a flow domain and the required boundary conditions has become a key bottleneck for numerical simulations. For external vehicle aerodynamics, the car industry at present is contemplating turnaround times of 1-2 days for arbitrary configurations. For so-called body fitted grids, the surface definition must be watertight , and any kind of geometrical singularity, as well as small angles, should be avoided in order to generate a mesh of high quality. This typically presents no problems for the main 'shape' of the car (the part visible to a streetside observer), but can be difficult to obtain in such a short time for the underhood and undercarriage of a typical car or truck. Experience indicates that even with sophisticated software toolkits, manual cleanup in most cases takes several days for a complete car. An alternative is to use grids that are not body-conforming, and simply 'embed' the triangulations of the wetted surfaces of the structures in them. Techniques of this kind are also known as immersed, embedded, fictitious domain or Cartesian methods. The treatment of points in the vicinity of the embedded CSD triangulations or CSD bodies is modified in such a way that the required kinetic or kinematic boundary conditions are properly

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